This invention relates to a repair construction and a method of repairing a damaged portion in the wall of a tire, particularly the sidewall of a radial tire.
Radial tires are constructed with radial wire cords which bear or absorb the loop tension from bead to bead due to internal air pressure when the tire is inflated. When one or more of the radial cords are broken due to tire damage, the loop strength must be restored in that local area in order to restore the proper load carrying capability of the tire.
One method of repairing such damaged areas in the walls of tires is to cut a section of the wall around the damaged portion to form a plug area, placing a patch over the plug area on the inside of the tire, and filling the remainder of the plug area with a plug material, such as uncured rubber. The plug material and patch then are cured to complete the repair except for final dressing.
The principal problem with repairs of the character described resides in the fact that such repairs result in a bulge in the repaired tire when its internal inflated pressure reaches road running conditions, for example, in truck tires a pressure of as much as 100 p.s.i. The bulge is mainly restricted to the plug area and might extend from the normal plane of the tire sidewall as much as one quarter inch or more under pressure. While such a bulge condition may not necessarily create or cause a functional or operational problem, it is totally unacceptable to many tire retailers, truckers and other end-users because the bulge is misconceived as a ply separation and because bulged tires may not pass many local and state inspections.
Various approaches have been attempted by the present inventors to eliminate this bulge problem encountered in tire repair constructions. In particular, different types or compositions of patches have been utilized, such as nylon, uncured rayon, semi-cured rayon, multiple-ply rayon, steel reinforced patches, and the like. Other types of patches have included woven nylon, criss-cross cord patches, and other well known patch materials and configurations. In all these instances, the particular patch material did not solve the bulge problem when the conventional repair method was employed.
Attempts have also been made by the present inventors to vary the modulus of the filler plug material, such as varying the durometer of the uncured plug material. These changes also failed to solve the bulge problem.
Other attempted solutions to the problem by the present inventors included adjusting the pressure differential inside and outside of the tire during curing, as well as varying the curing temperatures, but neither approach was successful in eliminating the resultant, undesirable bulges in the repair area.
Still another suggested solution made by others in the art was to grind or buff out the protruding bulge, but this results in a recess or "dimple" when the tire is uninflated which is a condition equally unacceptable to the retailer or trucker.